The Evidence on Sugar and Heart Disease

Documents reveal the sugar industry slanted the reserach.

Posted Sep 29, 2016

CC0 Public Domain
Source: CC0 Public Domain

The Evidence-Based Living blog relies strongly on systematic reviews to distill scientific evidence into information that people can use in their everyday lives. The idea is that researchers use sophisticated methods to evaluate the dozens, hundreds, or even thousands of articles on a topic. Review articles tell you exactly what methods were used to identify articles, how the articles were critically assessed and how the results were synthesized across studies.

At the end of that process, the researchers draw a conclusion based on the entire body of evidence on a topic. This is the most accurate way to assess what the data say on any given topic.  But what happens when a systematic review is wrong?

An article published earlier this month in the Journal of the American Medical Association poses this very question. In it, researchers use internal industry documents to describe how the sugar industry association — the Sugar Research Foundation — worked to skew a systematic review published in the New England Journal of Medicine in 1965 examining the links between diet and heart disease. The documents show that the sugar industry association influenced the review by excluding specific studies to minimize the link between sugar and heart disease, and put more of the blame on saturated fat.

The recent article raises serious questions about science and ethics — and specifically suggests that the scientific community give less weight to research funded by industry groups and corporations. In the meantime, what does the evidence say about the link between sugar and heart disease?

It turns out, there is strong scientific evidence that consuming sugar contributes to poor health and cardiovascular disease.

First, there is clear evidence that sugar consumption, and specifically consumption of sugar-sweetened beverages, is related to body weight.

In addition, several large systematic reviews document the relationship between sugar consumption and heart disease.

The U.S. Department of Agriculture's Nutrition Evidence Library published a review in 2015 that found  "moderate evidence" that increasing sugar intake, especially in the form of sugar-sweetened beverages, increases the risk of high blood pressure, stroke and heart disease among adults. A similar review published in the Journal of the American Medical Association in 2014 found "a significant relationship" between added-sugar consumption and deaths from heart disease. In fact, the American Heart Association recommends that all Americans reduce their consumption of added sugars.

But Americans find it difficult to even track, as well as limit, their intake of added sugar. According to the U.S. Centers for Disease Control, Americans consumed approximately 13 percent of their calories from sugar between 2005 and 2010.  The current dietary guidelines recommend that 10 percent or less of daily calories should come from added sugars.

It will soon become easier for Americans to gauge their sugar intake. This year, the U.S. Food and Drug Administration announced that it would change the requirements for nutrition labels, including documenting the amount of added sugars in foods. The new labels will be required on most packaged foods by 2018.

Reading those numbers should help consumers better understand what they are eating. Take, for example, a 20-ounce bottle of Coke. The current label explains that the drink contains 65 grams of sugar, which is 22 percent of the recommended carbohydrates for the day. But the new label will explain that those 65 grams of sugar are 130 percent the daily recommended value for added sugar.

What’s the take-home message here? There are several. First, it may be wise to be wary of industry-sponsored research. Beyond that, it is clear that consuming added sugars is a health threat that contributes to heart disease, diabetes, obesity, and stroke.